| Fitness index (FI) | F I = 1 - Σ ( Y i - Y ˆ i ) 2 / ( Y i - Y ¯ ) 2 |
| Bias | D ¯ = ∑ ( Y i − Y ^ ) / n |
| Standard error of estimate as percent of the mean (SEE%) | S E E % = ( e i − D ¯ ) 2 / ( N − 1 ) / Y ¯ × 100 |
| Mean absolute difference (MAD) | D ¯ = ∑ ( Y i − Y ^ ) / n |